Lipases are widely used in esterification of various carboxylic acids such as fatty acids with alcohols such as monoalcohols and polyalcohols, transesterification between esters of several carboxylic acids, and the like. Among them, the transesterification reaction is an important technology not only as method for modifying animal and vegetable fats and oils but also as method for producing esters of various fatty acids such as sugar esters and sterol esters. When a lipase, which is an enzyme hydrolyzing fats and oils, is used as a catalyst in the above reactions, the transesterification reaction can be conducted under the mild condition, i.e. at room temperature to about 70° C. Therefore, the reactions using a lipase can better inhibit side reactions and reduce energy costs as compared with the conventional chemical reactions. In addition to it, since a lipase as a catalyst is a natural product, it is highly safe. Further, intended compounds can be effectively produced by using a lipase due to the substrate specificity and positional specificity thereof. However, even if a powdery lipase is used in the transesterification reaction without change, activity thereof does not fully express. Besides, it is difficult to uniformly disperse a basically water-soluble lipase into oil raw materials and to collect such a lipase.
Therefore, generally, it is common to immobilize a lipase to some carriers, such as an anion-exchange resin (Patent Literature 1), a phenol adsorption resin (Patent Literature 2), a hydrophobic carrier (Patent Literature 3), a cation-exchange resin (Patent Literature 4) and a chelate resin (Patent Literature 5) and to use it in the reactions such as esterification and transesterification. Further, the method for producing immobilized lipase particles is proposed which comprises the steps of producing an emulsion wherein a water phase dissolving a lipase and a substance which acts as a carrier of a lipase is dispersing into a hydrophobic phase; and removing water from the emulsion to convert the water phase into solid particles thereof covered with the lipase (Patent Literature 6).
As mentioned above, a lipase has been conventionally immobilized and used in the transesterification reaction. However, the immobilized lipase loses an original lipase activity through the immobilization. In addition to it, when a porous carrier is used, a raw material or a product gets stuck in fine pores and, as a result, the transesterification rate decreases. Further, in the transesterification reaction wherein the conventional immobilized lipase is used, water which a carrier retains is brought into the reaction system, and therefore, it has been difficult to prevent side reactions such as production of diglycerides and monoglycerides in the transesterification reaction of fats and oils.
In light of the above situations, various technologies using a powdery lipase have been developed. For example, the method of the transesterification reaction is proposed which comprises the steps of dispersing a powdery lipase, in the presence or absence of an inactive organic solvent(s), into a raw material comprising an ester(s) so that 90% or more of the dispersed powdery lipase particles maintains a particle diameter of 1-100 μm during the reaction; and transesterifying said mixture (Patent Literature 7). Further, use of an enzymatic powder is also proposed, said enzymatic powder which is obtained by drying an enzyme solution comprising phospholipids and lipid-soluble vitamins (Patent Literature 8).
However, a powdery lipase of which lipase activity is further improved has been desired.
On the other hand, the method for producing an enzyme-immobilized preparation is proposed which comprises the steps of adding a grain powder or a grain powder and sugars to a solution comprising an enzyme(s), and drying the solution comprising an enzyme(s) (Patent Literature 9). The literature discloses that examples of usable enzymes include a lipase, a cellulase, a protease, an amylase and a pectinase, and that the enzyme-immobilized preparation obtained by the above production method can inhibit enzyme deactivation in the presence of a substance reducing an enzymatic activity. However, there is no description on the improvement of an enzymatic activity therein. Further, actually produced examples in the literature are only those in which a defatted soybean powder having less fat content is applied as a cellulase or a protease, and there is no specific description on an example wherein a lipase is used.
Patent Literature 1: JP-A 60-98984
Patent Literature 2: JP-A 61-202688
Patent Literature 3: JP-A 2-138986
Patent Literature 4: JP-A 3-61485
Patent Literature 5: JP-A 1-262795
Patent Literature 6: JP-B 3403202
Patent Literature 7: JP-B 2668187
Patent Literature 8: JP-A 2000-106873
Patent Literature 9: JP-A 11-246893